Since its discovery in 1982, the RAS family of genes has been characterized as an important class of proto-oncogenes (Cox et al., Nat. Rev. Drug Discov. 13:828 (2014)). Through three decades of extensive research, mutational activation of certain RAS genes (KRAS, NRAS, and HRAS) has been implicated in nearly one-third of all cancers (Pecot et al., Mol. Cancer Ther. 13:2876 (2014)). In particular, KRAS mutations are observed most frequently, both exclusively and in conjunction with the other RAS isoforms (Cox et al., Nat. Rev. Drug Discov. 13:828 (2014)). Yet in spite of efforts to develop inhibitors for this highly prevalent mutation, no strong therapeutic candidates have emerged, thus earning the KRAS gene its reputation as an elusively “undruggable” target.
The RAS genes encode a family of small GTPases that act upon downstream effector proteins to promote cell survival, growth, and proliferation (Khosravi-Far et al., Cancer Metastasis Rev. 13:67 (1994)). Proper function of the RAS proteins relies upon activation via a guanine nucleotide exchange factor (GEF) to its active, GTP-bound form as well as membrane association of the RAS-GTP complex, both of which have been proposed as targets for KRAS inhibition. However, due to low efficacy and target specificity of previously proposed therapeutic agents in directly inhibiting KRAS, current measures to target the KRAS, pathway focus predominantly on inhibition of downstream effector proteins (Cox et al., Nat. Rev. Drug Discov. 13:828 (2014)). Nevertheless, despite challenges in developing a small molecule to directly down-regulate gene activity, KRAS remains a therapeutically relevant target due to its prevalence as a driving mutation in human cancers.
Advances in RNA interference (RNAi) suggest its potential as an effective means of knocking down KRAS expression. RNAi therapy uses the interaction of an exogenous small interfering RNA (siRNA) and endogenous enzymatic machinery, termed an RNA-induced silencing complex (RISC), to selectively silence specific genes at the mRNA level (Pecot et al., Nat. Rev. Cancer 11:59 (2011)). A recent study has revealed the efficacy of RNAi as a well-tolerated therapy for inducing metastatic regression in human cancer patients (Tabernero et al., Cancer Discov. 3:406 (2013)). In addition, using nanoliposomes we have recently verified the efficacy of siRNA delivery for knockdown of human KRAS in various lung and colon cancer models, both in vitro and in vivo (Pecot et al., Mol. Cancer Ther. 13:2876 (2014)).
However, there remains a lack of target-specificity for mutant KRAS over the wild-type (WT) allele. Despite the oncogenic properties of the mutant allele, WT KRAS is necessary for proper response to extra-cellular inputs that promote viability in non-cancerous cells (Khosravi-Far et al., Cancer Metastasis Rev. 13:67 (1994)). As such, there is a need for inhibitors that target mutant KRAS while sparing WT KRAS.
Accordingly, the present invention overcomes the deficiencies in the art by providing compositions and methods using RNA interference for specific inhibition of mutant KRAS sequences.